Many factors, including environmental responsibility efforts and modern environmental regulations on engine exhaust emissions, have reduced the allowable acceptable levels of certain pollutants that enter the atmosphere following the combustion of fossil fuels. Increasingly, more stringent emission standards may require greater control over either or both the combustion of fuel and post combustion treatment of the exhaust. For example, the allowable levels of nitrogen oxides (NOx) and particulate matter have been greatly reduced over the last several years. To address, among other issues, environmental concerns, many diesel engines now have a diesel oxidation catalyst (DOC) as well as a diesel particulate filter (DPF) within an exhaust system of the diesel engine purposed to reduce the amount of NOx and particulate matter released into the atmosphere.
In some diesel engine operating conditions it may be beneficial to provide hydrocarbons, typically in the form of diesel fuel but other fuels or hydrocarbon sources may be utilized, to the exhaust system of the engine at a location upstream of the DOC such that the hydrocarbons will combust and raise temperatures within the DPF to a point sufficient to allow regeneration of the DPF. In other diesel engine operating conditions, it may be beneficial to provide hydrocarbons in the form of an in-cylinder post injection such that the exhaust is sufficiently warm to allow regeneration of the DPF to occur. However, in still other diesel engine operating conditions it may be beneficial to provide hydrocarbons both directly into the exhaust system and via in-cylinder post injection. Some engines are equipped with an injector to provide hydrocarbons both directly to the exhaust system, or via in-cylinder post injection.
However, one drawback of existing systems that provide hydrocarbons for DPF regeneration is to ensure that only a limited amount of hydrocarbons pass through the DOC without combusting, a condition often referred to as hydrocarbon slip. Hydrocarbon slip can have many negative effects on an exhaust system, such as causing the DPF to reach too high a temperature and break, causing a temperature hysteresis across the DOC, or blocking catalyst sites on the DOC and limit the DOC's ability to function properly. Therefore, a maximum amount of hydrocarbons that may be injected into the exhaust system for DPF regeneration must be controlled. Current attempts to control the maximum amount of hydrocarbon injection utilize calibration tables, but these tables were developed during steady state engine operating conditions, and therefore do not account for transient engine operating conditions.
Therefore, a need exists for a system and method of providing hydrocarbons to be used to raise exhaust temperatures that allow regeneration of a DPF to occur that allows delivery of hydrocarbons upstream of a DOC, but that calculates a maximum amount of hydrocarbons that may be delivered without causing hydrocarbon slip to exceed a preset limit.